Tunnel ram intake manifold for improved low RPM operation

ABSTRACT

A manifold including first and second divider bodies each having a carburetor mounting flange. The first divider body includes a first and a second plenum, and the second divider body includes a third and a fourth plenum. A first pair of runners extends from the first port flange to the first plenum; a second pair of runners extends from the first port flange to the third plenum; a third pair of runners extends from the second port flange to the second plenum; and a fourth pair of runners extends from the second port flange to the fourth plenum. Accordingly, in operation, each plenum will present only one carburetor venturi to the cylinder in a low-RPM, low-throttle opening induction event, thus keeping the peak velocity through the carburetor&#39;s venturi high even at low RPM.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/302,451, filed on Nov. 22, 2011, now allowed, which claims thebenefit of U.S. Provisional Patent Application No. 61/416,146, filedNov. 22, 2010, the disclosure of each of which is hereby incorporated byreference in its entirety.

BACKGROUND

In carbureted V-8 engines, a popular type of intake manifold for racingapplications is the tunnel ram. A tunnel ram intake manifold generallyfeatures a single large plenum to which eight intake runners connect tothe cylinder heads through a long straight path. Usually two 4-venturi,or barrel, carburetors are mounted to the top of the plenum. Thismanifold and carburetion combination is excellent for maximum powerproduction at high RPM, which is what is needed for racing engines. Thelength of the intake runners on a tunnel ram intake result in adistinctive tall intake manifold that usually extends through the hoodof the vehicle or requires the use of a large hood scoop.

Many automotive enthusiasts build vehicles (cars or trucks) for streetuse but want them to have the appearance of a racing vehicle. Thesevehicles are often referred to as “street rods.” Given its distinctiveappearance, many street rod enthusiasts would like to use the tunnel ramintake for its race car like appearance on their otherwise street tunedengine. However, the tunnel ram does not work well on most street tunedengines.

In order for a tunnel ram to work properly, the rest of the engine anddrive train should be specified for use with a tunnel ram intakemanifold. For example, for a tunnel ram to work well, the engine needsto be operated at a relatively high RPM, in the range of approximately3500-7000 RPM. For operation on the street, particularly with unmodifiedautomatic transmissions, low RPM performance below 3500 RPM isimportant. In street driving with OEM automatic transmission torqueconverter stall speeds, and gearing designed to keep RPM down for quietoperation and good fuel economy, the engine is nearly always operatingbelow 3500 RPM. Tunnel ram engines typically do not produce good torqueat low RPM. Thus, for street use in slow speed stop and go traffic atunnel ram equipped engine has poor drivability characteristics. Thereis no solution currently available which makes a tunnel ram intakemanifold suitable for low-RPM operation in a street application. In allcases, existing tunnel ram manifolds have unacceptable reductions inlow-RPM torque production.

Also, where the engine is unmodified or only slightly modified, theengine will not be able to operate at the higher RPMs required for thetunnel ram to reach its maximum potential performance benefits. Many OEMcamshafts are designed to produce good torque from idle to roughly 5000RPM. As mentioned above the tunnel ram is designed to work up to 7000RPM. Thus, with an OEM configured engine a large portion of the tunnelrams effective range is not used.

When used with electronic port fuel injection systems tunnel ram intakemanifolds work reasonably well in low-RPM street applications. With fuelinjection, a separate fuel injector is provided for each intake runner.This eliminates the poor fuel distribution problems associated withcarburetor tunnel ram combinations. In addition, the electronic computercalculates the fuel delivery needed under all conditions, usingelectronic sensors. However, electronic fuel injection has someimportant drawbacks for street rod use. First, it is expensive incomparison with a carburetion system. Secondly, the fuel injectors andtheir associated fuel rails dramatically change the appearance of theintake manifold system, and thus detract from the desired street rodappearance. The desire is typically to have a tunnel ram with two4-venturi carburetors. Fuel injectors detract from the authenticcarbureted racing engine appearance desired by street rod enthusiasts.Another drawback is that tuning electronic fuel injection in any non-OEMapplication requires knowledge, skills, and equipment that manyenthusiasts do not usually have available.

Accordingly, there is a need for a tunnel ram intake manifold that workswell with carburetors at lower engine operating speeds. Furthermore,there is a need for a device that allows a traditional tunnel ram intakemanifold to operate at lower engine speeds.

SUMMARY

Disclosed herein is a tunnel ram manifold, a divider body for use with aconventional tunnel ram base, and a tunnel ram intake manifold kit, allof which are useful for providing low RPM engine performance. In anembodiment, the tunnel ram manifold comprises first and second portflanges mateable to an engine, such as a V8 engine, for example. Theport flanges may be configured to mate with the cylinder heads of theengine.

The manifold includes first and second divider bodies each having acarburetor mounting flange. The first divider body includes a first anda second plenum, and the second divider body includes a third and afourth plenum. A first pair of runners extends from the first portflange to the first plenum; a second pair of runners extends from thefirst port flange to the third plenum; a third pair of runners extendsfrom the second port flange to the second plenum; and a fourth pair ofrunners extends from the second port flange to the fourth plenum.Accordingly, in operation, each plenum will present only one carburetorventuri to the cylinder in a low-RPM, low-throttle opening inductionevent, thus keeping the peak velocity through the carburetor's venturihigh even at low RPM. In an embodiment, the manifold further comprises ajoint located between each divider body and its associated runners.Thus, it is contemplated that the manifold may be integrally formed as aunitary body or may be comprised of multiple parts.

The first and second divider bodies each include a divider wall betweeneach divider body's respective plenums. Each divider wall may extendlongitudinally with respect to the engine. In an embodiment, each plenumincludes an inlet opening adjacent to its associated carburetor mountingflange converging to an aperture that is smaller than the inlet opening.This may be accomplished by including a pair of sloped surfaces, forexample, that extend from the inlet opening to the aperture. In anembodiment, the inlet opening is obround in shape and the aperture maybe rectangular in shape.

In another embodiment, the tunnel ram manifold comprises first andsecond port flanges and first and second divider bodies. The firstdivider body includes a first and a second plenum, and the seconddivider body includes a third and a fourth plenum. A first runnerextends from the first port flange to the first plenum; a second runnerextends from the second port flange to the first plenum; a third runnerextends from the first port flange to the second plenum; a fourth runnerextends from the second port flange to the second plenum; a fifth runnerextends from the first port flange to the third plenum; a sixth runnerextends from the second port flange to the third plenum; a seventhrunner extends from the first port flange to the fourth plenum; and aneighth runner extends from the second port flange to the fourth plenum.In this embodiment, the first and second divider bodies each include adivider wall between each divider body's respective plenums that extendstransversely with respect to the engine.

Also disclosed herein is a divider body for use with a conventionaltunnel ram base. In an embodiment, the divider body comprises a mountingflange securable to a conventional tunnel ram base. The divider bodyincludes a carburetor flange and a body portion extending between themounting flange and the carburetor flange. A divider wall separates thebody portion into two plenums. In an embodiment, the mounting flange isconfigured such that the divider wall extends longitudinally withrespect to the conventional tunnel ram base when the mounting flange issecured thereto. The mounting flange may be configured such that thedivider wall extends transversely with respect to the conventionaltunnel ram base when the mounting flange is secured thereto.

Also disclosed is a tunnel ram intake manifold kit. The kit comprises atleast one divider body and at least one carburetor. The divider bodycomprises a mounting flange securable to a conventional tunnel ram baseand a carburetor flange for mounting the carburetor. A body portionextends between the mounting flange and the carburetor flange and adivider wall separates the body portion into two plenums. The kit mayinclude a pair of divider bodies and a pair of carburetors. In anembodiment, the kit also includes a conventional tunnel ram base.

These and other aspects of the tunnel ram intake manifold will beapparent after consideration of the Detailed Description and Figuresherein.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of an improved tunnelram intake manifold and together with the description, serve to explainthe principles and operation thereof. Like items in the drawings aregenerally referred to using the same numerical reference.

FIG. 1 is a side view in elevation of a tunnel ram intake manifoldaccording to a first exemplary embodiment with associated carburetorsand air cleaners attached thereto;

FIG. 2 is a top plan view of the base portion of the tunnel ram intakemanifold shown in FIG. 1;

FIG. 3 is a is a top plan view of a tunnel ram intake manifoldconfigured for sideways carburetor mounting;

FIG. 4 is a perspective view of the divider body shown in FIG. 1 asviewed from the top;

FIG. 5 is a perspective view of the divider body shown in FIGS. 1 and 4as viewed from the bottom;

FIG. 6 is a side view in elevation of the divider body shown in FIGS. 1,4 and 5;

FIG. 7 is a top plan view of the divider body shown in FIG. 6;

FIG. 8 is a bottom plan view of the divider body shown in FIG. 6;

FIG. 9 is a cross-sectional side view of the divider body taken aboutline 9-9 in FIG. 7;

FIG. 10 is a cross-sectional side view of the divider body taken aboutline 10-10 in FIG. 7;

FIG. 11 is a top plan view of a tunnel ram intake manifold configuredfor front-to-back carburetor mounting;

FIG. 12 is a top plan view of a converging plenum according to anexemplary embodiment;

FIG. 13 is a cross-sectional view of a divider body according to asecond exemplary embodiment with a divider wall that extends onlypartially down the length of the body;

FIG. 14 is a top plan view of a funnel body according to an exemplaryembodiment;

FIG. 15 is a cross-sectional view of the funnel body taken about lines15-15 in FIG. 14;

FIG. 16 is a side view in elevation of a tunnel ram manifoldconfiguration that employs a pair of funnel bodies shown in FIG. 14along with a traditional tunnel ram common plenum;

FIG. 17 is a perspective view of a common plenum according to anexemplary embodiment; and

FIG. 18 is a side view in elevation of a tunnel ram manifoldconfiguration that employs the common manifold shown in FIG. 17.

DETAILED DESCRIPTION

Provided herein is an improved tunnel ram manifold design that improvesthe low RPM performance of the traditional tunnel ram manifold bydividing the large single plenum of the tunnel ram into four separateplenums, each connected to only two intake runners. The low RPMperformance is thereby improved while maintaining the distinctive racecar appearance of the tunnel ram, which is of paramount importance tothe typical street rod enthusiast.

A carburetor meters the appropriate amount of fuel according to enginedemand based on intake air flow into the engine. Carburetors operate onthe principle that as the velocity of air flow increases, its pressuredecreases. Carburetors are configured to take advantage of the pressuredifferential created between atmospheric pressure surrounding thecarburetor and a low pressure region created inside the carburetor,usually by way of a venturi. As an engine draws more air through theventuri the low pressure region (i.e. signal) created by the increasingair velocity draws a metered amount of fuel into the intake air flowstream.

With a single large plenum design like the traditional tunnel ram (alsocalled a single plane design), each induction event goes through two ormore venturis. A traditional tunnel ram intake has a single large plenumenclosed by a cover that includes two 4-barrel carburetor mounts. Thus,each induction event draws air through multiple venturis depending onthe type of carburetors employed. An example of traditional single planetunnel ram manifolds includes the Victor Ram, Part No. 7070, marketed byEdelbrock® of Torrance, Calif. When an induction event goes through twoor more venturis it reduces the air velocity through those venturis,which in turn reduces the strength of the signal to the fuel meteringsystem. The weakened signal through the venturis of a tunnel ramcarburetion configuration accounts for the poor low RPM performancedescribed above. This situation is exacerbated by the presence of two4-venturi carburetors on the typical tunnel ram. In this situation, fourventuris are flowing air even at part throttle operation, and the signalto each venturi is very weak. Therefore fuel metering at low RPM ispoor.

Because low RPM operation is important in street applications, nearlyall OEM V8 engines with carburetion use a dual-plane intake manifold,such as the Performer RPM, Part No. 7101, also marketed by Edelbrock® ofTorrance, Calif. This type of manifold usually uses a single carburetor,though a few examples with dual carburetion exist. The dual-planemanifold feeds four cylinders from one half of the carburetor throughone side of the manifold, and the other four from through the otherside. Half of the carburetor means a single primary and a singlesecondary venturi, for a 4-venturi carburetor. For example, on aChevrolet V8 engine, cylinders 1, 4, 6, and 7 are fed from one side ofthe carburetor, while cylinders 2, 3, 5, and 8 are fed from the otherhalf. Other commonly available V8 engines with cruciform crankshafts usesimilar dual-plane intake manifolds.

The dual-plane intake manifold provides good low RPM performance becauseeach intake runner is only connected to half of the carburetor. Thus atlow-RPM part-throttle operation, when only one venturi is operating ineach half of the carburetor, the induction event goes through oneventuri. This results in higher velocity of air through that singleventuri, which gives the fuel delivery system a strong metering signal.

Tunnel ram intake manifolds do exist that have two separate plenums. Inother words, cylinders 1, 2, 3 and 4 are fed by one carburetor, while 5,6, 7, and 8 are fed by a second carburetor. This manifold configurationstill suffers from low RPM performance problems related to a weakmetering signal. Conventional tunnel rams are also available with asingle carburetor mounting pad, but again two venturis are connected toa given cylinder at part throttle. In addition, the large plenum belowthe carburetor or carburetors in a conventional tunnel ram is very goodfor producing power at high RPM, but results in poor fuel distributionamong the cylinders at low RPM. This is often compensated for by runninga richer air-fuel mixture. However, running a richer air-fuel mixtureoften results in fouled spark plugs.

In order to address the limitations of traditional tunnel ram intakedesigns as explained above, an improved tunnel ram manifold design isprovided that improves low RPM performance by dividing the large singleplenum of the tunnel ram into four separate plenums. FIG. 1 illustratesa tunnel ram intake manifold 20 according to a first exemplaryembodiment. In this embodiment, tunnel ram 20 includes a base portion 22that includes a plurality of intake runners 24 and a pair of dividerbodies 40(1) and 40(2) disposed thereon. Base portion 22 may comprisethe base portion from a traditional tunnel ram intake manifold. Forexample, the base portion from a Weiand® Hi-Ram manifold, model no.1984, is a suitable base portion (the base portion is availableseparately from Weiand® as part no. 5984). The Weiand® manifold isdescribed in U.S. Pat. No. 3,561,408, the disclosure of which is herebyincorporated by reference in its entirety. As shown in FIG. 1, thetunnel ram manifold 20 is fitted with a pair of carburetors 82(1), 82(2)and a pair of velocity stacks 84(1), 84(2). In this case, thecarburetors are 580CFM vacuum secondary carburetors available from QuickFuel Technology. The carburetors may be tuned for a particular manifoldconfiguration as necessary by adjusting the jets, emulsion circuit, airbleeds, power valve, and secondary spring settings, all of which arewell understood in the art of carburetor tuning.

With further reference to FIGS. 2 and 3, tunnel ram manifold 20 includeseight intake runners 24 corresponding to the cylinders of an eightcylinder engine. The cylinders relative locations are labeled in thefigures as cylinders 1-8. While the tunnel ram manifold is describedherein with respect to an eight cylinder engine application, a tunnelram according to the present disclosure may be used on other engineconfigurations with different multiples of cylinders. In thisapplication, pairs of the eight intake runners 24 each communicate withone of four separate plenums 44. With particular reference to FIG. 3,each divider body 40(1) and 40(2) is divided by a plenum divider 42 intofirst and second plenums 44(1) and 44(2). Accordingly, the tunnel ram 20includes four separate plenums each communicating with only two intakerunners 24. This example pairs cylinders as follows: 1-2, 3-4, 5-6, and7-8.

In operation, each of these plenums 44 will present only one venturi tothe cylinder in a low-RPM, low-throttle opening induction event, thuskeeping the peak velocity through the venturi high even at low RPM.Dividing the plenum may affect peak power output, but does not limit thehigh RPM performance of the typical street rod engine. Even for racingapplications, this style of four-plane manifold may be suitable whencombined with larger capacity carburetors. Carburetors are availablewith a range of venturi sizes to suit engines of varying airflowcapacity. For example, a few suitable 4-venturi carburetors are soldunder the Holley, Edelbrock, and Barry Grant brand names, and rangebetween 390CFM and 1250CFM in airflow rating.

Tunnel ram 20 comprises a tunnel ram configuration having two separatebodies 44(1), 44(2) that are each divided in half as explained above.FIG. 2 shows base portion 22 of tunnel ram 20 illustrating the groupingof cylinder intake runners 24. The inlets 26 of each intake runner groupare arranged together with wall 23 between them for coupling to thedivider bodies and ultimately the carburetors. Each runner extends froma corresponding inlet 26 to an associated port flange 27 (see FIG. 1).With further reference to FIGS. 3-5, a divider body 40 mates with eachgroup of intake runner inlets 26. Divider body 40(1), for example,includes two plenums 44(1) and 44(2) separated by divider 42. In thiscase, divider 42 extends transversely to the centerline of the engine(i.e. crankshaft) and manifold (see FIG. 3). The divider may also beoriented parallel to the centerline of the engine as is described morefully below.

As shown in FIG. 6, each divider body 40 includes a carburetor flange 45and a mounting flange 47 with a body portion 46 extending therebetween.Carburetor flange 45 includes a plurality of mounting apertures 65.Mounting apertures 65 may be plain bores or threaded bores for receivinga suitable carburetor mounting fastener. Mounting flange 47 includes apair of holes 67 for mounting the divider body to the manifold base 22.As shown in FIG. 10, mounting flange 47 includes a pair of inwardlyprojecting tabs 68 through which holes 67 are formed. However, the tabscould project outwardly from the divider body for differentapplications.

With further reference to FIGS. 7 and 9, each plenum includes slopingwall portions 56(1) and 56(2). Thus, each plenum has a larger inletopening 55 which funnels or converges via wall portions 56(1), 56(2) toa smaller aperture opening 58. Accordingly, the fuel/air mixture isguided to the center of the plenum. Guiding the fuel/air mixture to thecenter of the plenum provides even fuel distribution between the runnersconnected to the plenum. In this case, the inlet opening 55 is obroundin shape. Aperture openings 58 are, in this case, rectangular openingswith a length Z, which is approximately equal to the width of eachplenum 44, and a width Y. In this case length Z is approximately 1.75inches and the width Y is approximately 1.375 inches. It should beunderstood that the shape and dimensions of the inlet and apertureopenings of the plenums may vary depending on the particular engine andoperating characteristics desired. For example, enlarging the apertureopening 58 may increase peak horsepower but potentially at the expenseof low RPM drivability. With reference to FIGS. 8 and 9, each plenumalso includes sloping wall portions 57(1) and 57(2). Each plenumdiverges via wall portions 57(1), 57(2) from aperture opening 58 tooutlet opening 59.

Referring again to FIG. 1, it can be appreciated that the tunnel ram 20may comprise several components that are bolted together. In this case,the manifold 20 comprises a base portion 22 and a pair of divider bodies40(1) and 40(2) that are each bolted to the base portion at a joint 32.However, the manifold may be cast as one piece with the appropriatedividers in place such that only two intake runners are fed by half ofeach carburetor. Furthermore, it will be appreciated by those skilled inthe art that portions of existing traditional tunnel ram intakemanifolds may be replaced with divider plates or divider bodiesaccording to the present disclosure, thereby improving the low RPMperformance of existing tunnel ram installations. Moreover, differenttunnel ram configurations may be divided into the four separate plenumsas described herein. For example, the traditional single plenum tunnelram manifold (such as the above mentioned Victor Ram from Edelbrock) maybe retrofitted with a new cover that includes appropriate dividers tocreate four separate plenums. Appropriate dividers may comprise foamrubber in order to comply with the rough casting surface of suchmanifolds. The tunnel ram may be cast from a suitable metal, such asaluminum or steel for example. Furthermore, the tunnel ram may becomprised of plastic or composite material. The tunnel ram may befabricated from metal, plastic, or other suitable material and/orprocess.

Those ordinarily skilled in the art are aware that 4-barrel carburetorsoften have a pair of primary venturis and a pair of secondary venturis.The primary venturis are used for low load operation while all fourventuris are activated for high load operation. As can be appreciated inFIG. 3, the transverse orientation of divider 42 means that the intakemanifold is, in this case, set up for the carburetors to be mounted“sideways”, that is with the primary venturis on one side of the engineand the secondary venturis on the other side. This is referred to as“sideways” by those skilled in the art because the conventional way tomount the carburetor is to have the primary venturis face the front ofthe engine (and the front of the vehicle, in conventional,non-transverse engine mounting). With transversely oriented dividers,mounting the carburetor sideways means that each pair of cylinders isfed by both a primary and a secondary venturi. Otherwise, one pair ofcylinders would only be fed by primary venturis and another pair ofcylinders would only be fed by secondary venturis. Mounting thecarburetor sideways and having transverse dividers means that eachplenum feeds opposed cylinders. For instance, cylinders 1 and 2 sharethe same plenum.

Sideways mounting is a way to accommodate larger carburetors in a dualcarburetor setup. Those skilled in the art will appreciated that onHolley “double pumper” carburetors, for example, which have mechanicallyactuated secondary venturis, the fuel bowls extend out far enough thatthey cannot be mounted front-to-back except on very large “big-block”engines; thus, sideways mounting is necessary. Double pumpers are usedfor racing, and thus are popular street rod items even though they areless suited to street operation than single-pump, vacuum secondarycarburetors. Carburetors have accelerator pumps to enrich the air-fuelmixture when the throttle is opened. An accelerator pump is a smallbellows pump that squirts fuel down the venturi when the throttle isopened. The accelerator pump keeps the mixture from leaning out onthrottle opening. Without it, when the throttle is opened, the air flowrises instantly but it takes the fuel metering signal a second or so tocatch up, which results in a lean stumble. All 4-venturi carburetorshave accelerator pumps on the primaries. Street car carburetors have thesecondaries controlled by a mechanism that senses airflow and opens thesecondaries slowly as demand rises, so they do not need an acceleratorpump on the secondaries. “Double pumpers” open the secondaries with thethrottle lever regardless of airflow demand from the engine, andtherefore require an accelerator pump for the secondaries as well. Theyare also called mechanical secondary carburetors. Many street engineconfigurations use a vacuum secondary carburetor for drivability andfuel economy. However, street rod enthusiasts prefer to use the dualcarburetor setup with a pair of double pumper carburetors for theirracing appearance. To implement such a setup on a small-block V8requires sideways mounting.

As mentioned above, the dividers may, as an alternative, be orientedparallel to the centerline of the engine. FIG. 11 illustrates a manifoldconfigured for use with carburetors mounted front to back. In this casedivider bodies 40(1) and 40(2) are oriented such that the dividers 42extend parallel to the engine and manifold. Accordingly, each dividerbody 40 includes a pair of plenums 44(1) and 44(2) separated by divider42. Thus, the cylinders are paired into four plenums as follows: 1-3,2-4, 5-7, and 6-8.

Also contemplated herein is a converging plenum 102, shown in FIG. 12,which is similar to the above-described divider bodies such as shown inFIGS. 4-10. However, in this case, the converging plenum 102 does notinclude a divider wall. Accordingly, the converging plenum 102 has asingle plenum 114. Plenum 114 includes a pair of sloping wall portions106(1) and 106(2) that converge to an aperture 108. The plenum convergesfrom an inlet opening 105 via sloping wall portions 106(1) and 106(2) tothe aperture opening 108. In an embodiment, the converging plenum 102may include diverging wall portions similar to those described abovewith respect to FIGS. 8 and 9. Converging plenum 102 could be used incertain applications in place of the divider body 40 described above inorder to improve fuel distribution.

FIG. 13 illustrates another exemplary embodiment of a divider body 140that, like divider body 40 described above, includes a pair of plenums144(1) and 144(2) that are separated by divider wall 142. However, inthis case, the divider wall 142 does not extend all the way down thedepth of body portion 146. Accordingly, the plenums 144(1) and 144(2)intersect a common plenum 145 within the body portion 146. Thisconfiguration allows a certain amount of airflow sharing between theventuris of the associated carburetor. The amount of airflow sharing maybe varied by adjusting how far down the body portion 146 divider wall142 extends. For example, in this embodiment, the divider wall 142 mayextend approximately half way down the body portion. Divider body 140could be used in certain applications in place of the divider body 40described above.

FIGS. 14 and 15 illustrate a funnel body 240 that is similar to thedivider body 40 described in FIGS. 4-10 in that it includes sloping sidewalls 256(1) and 256(2) that extend towards an aperture 258; however, inthis case, aperture 258 is the outlet and there are not divergingsloping sidewalls (see FIG. 15). This configuration of divider body isuseful when paired with a traditional common plenum 200, an example ofwhich is shown in FIG. 16. A suitable common plenum is available fromWeiand® (part No. 1912) and attaches to the base portion 22. As shown inFIG. 16, a pair of funnel bodies 240(1), 240(2) are disposed between thecommon plenum 200 and carburetors 82(1), 82(2). In this embodiment, thefunnel bodies 240 include a pair of plenums 244(1) and 244(2) separatedby divider wall 242. As mentioned above, each plenum 244(1), 244(2)includes a pair of sloping side walls 256(1), 256(2) that converge to anoutlet aperture 258. As in previous embodiments, the inlet opening 255is obround in shape and converges to a generally rectangular outletaperture 258. This configuration allows a certain amount of airflowsharing between the carburetors. The amount of sharing may be adjustedby varying the volume of the plenum, which may be accomplished byvarying the height of the plenum, or by adding material to the centersection between the runners to take up volume inside the common plenum.

FIG. 17 illustrates a common plenum 340, according to an exemplaryembodiment, that is adapted for use with divider bodies 40 as shown inFIG. 18. The common plenum 340 is disposed between the divider bodies 40and carburetors 82. As shown in FIG. 17, the common plenum 340 includesa pair of plenum chambers 344(1) and 344(2) that are connected by tunnel350, which has an interior 352. Accordingly, plenums 344(1) and 344(2)are in fluid communication with each other via tunnel 350. As shown, thecommon plenum 340 is configured with standard carburetor mountingflanges, as are known in the art, with mounting surfaces 345, 347, andassociated mounting holes 365. Providing a small single plenum on top ofthe existing four-plenum structure allows some airflow sharing betweenthe carburetors under high-RPM, high-load operation. Accordingly, thevacuum and flow variations seen by each carburetor will be reduced,thereby allowing the use of carburetors with a more off-the-shelf tunewith respect to the emulsion circuit, air bleeds, power valve, andsecondary spring. The height of plenums 344(1), 344(2) may be changed toprovide a trade off between low-RPM performance and high-RPMperformance.

While the tunnel ram has been described in the various embodiments,constructions, and configurations as a complete manifold, it is alsocontemplated that various retrofit components could be provided that areoperative to modify existing tunnel ram intake manifolds. These retrofitcomponents could be in the form of individual bolt on components or inkit form including instructions and ancillary items such as suitablysized carburetor jets, air bleeds, and emulsion tubes for a particularapplication. In an embodiment, the kit comprises at least one dividerbody 40(1) and at least one carburetor 82(1). With reference to FIG. 1,the kit may include a pair of divider bodies 40(1), 40(2) and a pair ofcarburetors 82(1), 82(2). In an embodiment, the kit also includes aconventional tunnel ram base 22. Furthermore, the kit may includeassociated air cleaners and/or velocity stacks 84(1), 84(2).

Also, contemplated are methods for retrofitting an engine with animproved tunnel ram intake according to the present disclosure. Themethods thus encompass the steps inherent in the above describedmechanical structures and operation thereof. Broadly, one method couldinclude removing the top plate or divider bodies of a conventionaltunnel ram and replacing it with divider bodies or a top plate havingappropriate dividers according to the teachings herein.

Accordingly, the improved tunnel ram intake manifold has been describedwith some degree of particularity directed to the exemplary embodiments.It should be appreciated, though, that the technology of the presentapplication is defined by the following claims construed in light of theprior art so that modifications or changes may be made to the exemplaryembodiments without departing from the inventive concepts containedherein.

What is claimed is:
 1. A tunnel ram manifold, comprising: first andsecond port flanges mateable to an engine; first and second convergingplenums each having a carburetor mounting flange; a first pair ofrunners extending from the first port flange to the first convergingplenum; a second pair of runners extending from the first port flange tothe second converging plenum; a third pair of runners extending from thesecond port flange to the second converging plenum; and a fourth pair ofrunners extending from the second port flange to the first convergingplenum; wherein each converging plenum includes an inlet openingadjacent its associated carburetor mounting flange converging to anaperture smaller than the inlet opening.
 2. The manifold according toclaim 1, wherein each converging plenum includes a pair of slopedsurfaces extending from the inlet opening to the aperture.
 3. Themanifold according to claim 1, wherein each aperture is rectangular inshape.
 4. The manifold according to claim 3, wherein each rectangularaperture extends longitudinally with respect to the engine.
 5. Themanifold according to claim 1, further comprising a joint between eachconverging plenum and its associated runners.
 6. A converging plenum foruse with a conventional tunnel ram base, the plenum comprising: amounting flange securable to a conventional tunnel ram base; acarburetor flange; a body portion extending between the mounting flangeand the carburetor flange; and an inlet opening adjacent the carburetorflange converging to an aperture smaller than the inlet opening.
 7. Theplenum according to claim 6, including a pair of sloping wall portionsextending from the inlet opening to the aperture.
 8. The plenumaccording to claim 7, wherein the mounting flange is configured suchthat the pair of sloping wall portions extend longitudinally withrespect to the conventional tunnel ram base when the mounting flange issecured thereto.
 9. The plenum according to claim 7, wherein themounting flange is configured such that the pair of sloping wallportions extend transversely with respect to the conventional tunnel rambase when the mounting flange is secured thereto.
 10. The plenumaccording to claim 7, including a pair of diverging wall portionsextending from the aperture to the mounting flange.
 11. A tunnel ramintake manifold kit, comprising: at least one converging plenum,comprising: a mounting flange securable to a conventional tunnel rambase; a carburetor flange; a body portion extending between the mountingflange and the carburetor flange; and an inlet opening adjacent thecarburetor flange converging to an aperture smaller than the inletopening; and at least one carburetor mountable to the carburetor flange.12. The tunnel ram intake manifold kit according to claim 11, includinga pair of converging plenums and a pair of carburetors.
 13. The tunnelram intake manifold kit according to claim 12, including a conventionaltunnel ram base.
 14. The tunnel ram intake manifold kit according toclaim 11, including a pair of sloped surfaces extending from the inletopening to the aperture.
 15. The tunnel ram intake manifold kitaccording to claim 14, wherein the aperture is rectangular in shape.